1. Field of the Invention
The present invention relates to an air bag system for inflating an air bag when impact or deformation is sensed in the event of a vehicle collision and more particularly, to a modular cover adapted to accommodate an air bag in the system.
2. Description of the Related Art
A conventional modular cover for use in an air bag system comprises a rigid inner layer 11, and a soft outer layer 12 as illustrated in FIG. 4. The modular cover is provided with a tear line 13 so that the modular cover is torn along the tear line 13 when the air bag is inflated. The modular cover is made by a two-color molding process wherein two resins are separately injected into a common mold.
During the two-color molding process, such a modular cover, composed of the inner and outer layers as shown in FIG. 4, is subject to shrinkage (sink mark or depression) when the resins are cured.
Specifically, depression (shrinkage) results from curing of the outer layer 12 as shown in FIG. 5. FIG. 5 is an enlarged view of a portion V of the modular cover shown in FIG. 4. The depression causes dimples"A"on a surface 12a of the outer layer 12 adjacent to the tear line 13. This deteriorates the appearance of the modular cover. The arrows"B"show the directions in which the material shrinks.
U.S. Pat. No. 5,172,931 for Baba et.al. discloses an modular cover for an air bag system to prevent the outer layer 12 from forming dimples produced by the depression during the molding process of the outer layer 12. The modular cover is provided with projections 14 disposed on the surface of the inner layer 11 which abuts the outer layer 12, adjacent to the tear line 13 so as to prevent the outer layer 12 form forming dimples as shownin FIG. 6.
In the modular cover for an air bag system of Baba et. al., the projections 14 for preventing the outer layer 12 from forming dimples are provided on the surface of the inner layer 11 which abuts the outer layer 12, thereby the shrinkage stress produced during curing of the outer layer 12 is dispersed so as to prevent the outer layer 12 from partly producing the dimples on the surface adjacent to the tear line 13.
According to the modular cover of Baba et.al., when a resin is injected into a mold for the outer layer after curing of the inner layer, each projection 14 becomes an obstacle to the flow S of the resin to produce a turbulent flow"M"at the back of the projection 14 as shown in FIG. 7. FIG. 7 is an enlarged top view of a portion around one of the projections 14. The turbulent flow"M"causes a defective product after curing.